Surgical implantation of artificial sphincters has often been employed to treat patients suffering from urinary incontinence. The surgical implantation of the artificial sphincter commonly requires hospitalization. In addition, such a procedure is relatively complex and expensive, and will usually require six to eight weeks of recovery time. Moreover, often time, the procedure is unsuccessful or the artificial sphincter malfunctions. As a result, additional surgery is required to adjust, repair or replace the implant.
In the recent past, urinary incontinence may be successfully treated by using nonsurgical means. A common and widely used method to treat patients with urinary incontinence is periurethral injection of a composition commercially sold in Canada as "Polytef" and as "Urethrin". "Polytef" is a paste comprising a fifty-fifty (50/50) by weight mixture of glycerine liquid and Teflon particles. However, after injection, over a period of time the glycerine is readily dissipated into the body and then metabolized or eliminated, leaving only the Teflon particles. This means that only fifty (50) percent of the injected weight remains at the injection site. Consequently the surgeon must inject significantly more volume than he thinks he will need and at times must actually close down the urethra further than is desired. This closure could possibly be complete and thus put the patient into temporary urinary retention. Additionally, the fact that a large portion of the volume disappears makes it difficult for the surgeon to visually gauge how much is an appropriate amount of the Teflon paste to inject. As a result, the surgeon is likely to not inject enough paste volume. The procedure therefore may fail, and a second or even a third procedure to inject additional paste may be required. An additional drawback of the Teflon paste is that the Teflon particle size is sufficiently small so as to allow the particles to migrate to other locations of the body such as the lungs, brain, etc. Teflon particles have been known to induce tissue reaction and form Teflon-induced granulomas in certain individuals. This tissue reaction to Teflon has caused concerns for the patient's safety. Also, the Teflon paste is highly viscous and can only be used by applying a large injection force (IF) injected using a hypodermic held by an injection assist device since the surgeon would not have sufficient strength to force the highly viscous Teflon paste through a needle of any acceptable size.
An alternative to using the Teflon paste is using a collagen suspension. The collagen suspension is injected in the same manner as Teflon paste so as to form a fibrous mass of tissue around the augmentation site. This fibrous mass created by the collagen injection, however, decreases in size and breaks down over time as it is eventually degraded by the patient's body. As a result, additional injections are periodically required.
Another alternative is to inject silicone particles dispersed in an aqueous, polyvinylpyrrolidone solution. This combination has the same problems as the Teflon paste in that the polyvinylpyrrolidone solution is readily dissipated away from the area of injection leaving only the volume of silicone particles remaining and in that due to its high viscosity a great deal of force is necessary to inject the silicone dispersion through a needle of an acceptable size whereby it is necessary for the surgeon to utilize an injection assist device to accomplish injection.
Another material that has been injected is autologous fat. This has had similar problems as the collagen in that the body eventually breaks it down and it disappears.
Devices have been made to attempt to overcome these problems. One device is an inflatable silicone sphere that is passed through a needle and is inflated with saline in the same area that the other materials are injected. There are, however, some problems associated with this device. It is a delicate, mechanical device that is capable of mechanical failure of the valves, shells and structural joints.
Accordingly, it would be desirable to have a composition which has sufficiently low injection force so that it is not necessary to utilize an injection assist device to inject it whereby it is easily administered via injection, generally will not change in volume following insertion, will be soft enough so as to not cause tissue response/reaction while still being firm enough to provide the required constriction, will not dissipate and will not migrate from the site of injection, thereby enabling the urethra to maintain the initial surgical constriction.
Berg, et al., in U.S. Pat. No. 5,007,940 have made an attempt to overcome the above set forth problems by utilizing fully hydrated hydrogel particles in disk form which deform as they pass through a needle during injection. The cost to synthesize such particles has, however, been so high that they have not been utilized commercially. Also, the particles have still exhibited a significantly high viscosity whereby their use has required the use of relatively large internal diameter needles and the use of relatively large injection forces to accomplish insertion in a patient. Thus, they have not served to fully overcome the problems of the prior art.